1. Field of Invention
The invention relates to the suspension of solid particles in a predetermined volume of liquid, the particles and the volume of liquid being contained together inside a container which is itself delimited by a wall and to the suspension or resuspension of particles, forming a deposit adhering to the internal face of the wall of the container, in the form of a continuous film or of aggregates, and bringing together at least some of these particles in the agglomerated state, and doing so in a predetermined volume of the liquid, contained inside the container.
2. Description of Related Art
The physical state of particles /liquid defined above is encountered in particular in certain biological analyses, using particles of a size equal to no more than 10 xcexcm, and preferably of between 0.01 xcexcm and 10 xcexcm, for example between 1 and 5 xcexcm, these particles comprising a magnetic substrate on which there is fixed at least one analyte, or at least one reagent, and being dispersed in a continuous liquid phase, for example an aqueous phase. In fact, the separation of these particles, under the effect of a magnetic field, from the liquid phase leads in part to their accumulation and agglomeration in the form of a continuous or discontinuous deposit adhering to the internal face of the wall of the container. In such cases, in order to continue the analysis and obtain reliable, reproducible and precise results, it is essential to break up the deposit in order to resuspend the particles in the predetermined volume of the liquid, in the container, for example a micro vessel for analysis, as otherwise the particles collected, and to an extent separated off in the deposit on the wall, cannot participate in the remainder of the analysis process or protocol.
The deposit of agglomerated particles on the wall of the container is conventionally broken up by introducing a complementary flow of liquid, for example under pressure, into the container, and more precisely into the liquid volume, in such a way as to entrain and suspend the previously agglomerated particles, by hydrodynamic action. This solution has the major disadvantage of adding to the container a certain quantity of liquid phase which, even if controlled or predetermined, brings about a dilution of the particles, which dilution reduces the sensitivity of the analysis procedure used.
GB-A-1 330 975 and DE-A-3 233 926 disclose a method for suspending solid particles in a predetermined volume of liquid, contained inside a container delimited by a wall, which latter may become partly isolated from the heart of the liquid by a deposit adhering to its internal face, and bringing together at least some of the particles in the agglomerated state. According to this method, the container is simultaneously subjected to a reciprocating movement along a reference axis and to a magnetic field turning about the said reference axis.
The previously described method is specific to magnetic particles and can be used only with such particles, since it is the conjunction of the rotational movement of the particles, generated by the rotating magnetic field, and the relative reciprocating translational movement, between the field and the container, which detaches and disperses any deposit of the magnetic particles likely to agglomerate on the internal face of the container.
An object of the invention is therefore a method for suspending particles, starting from the physical state described or defined above, independently of the nature of the particles, and mechanically or hydrodynamically, without introducing a supplementary quantity of liquid into the container.
According to the invention, it has been discovered, in a totally surprising manner, that by subjecting the container exclusively to a reciprocating movement along a reference axis, and at a relatively high frequency, at least equal to 10 Hz, produces, within the predetermined volume of liquid, and without any other external action being needed (in particular a magnetic field), an ebb/flow resonating against the wall of the container on either side of the reference axis, breaking up the deposit adhering to the internal face of the wall of the container, and dispersing the broken up particles toward the center of the volume of liquid.
Thus, by means of the invention, it is possible to completely break up the parasitic deposit with the sole aid of the volume of liquid contained in the container, this remaining constant and predetermined.
The solution according to the invention affords another advantage too.
The maximum height of the ebb/flow obtained according to the present invention makes it possible to mechanically sweep and detach agglomerated particles from the internal face of the container above the normal level (at rest) of the liquid contained in the said container, even with a small quantity of liquid.